1. Technical Field
The present invention relates to a light scanning apparatus which deflects a light beam using an oscillation mirror and makes the light beam scan in a main scanning direction, and also to a method of controlling such an apparatus. The present invention relates to an image forming apparatus having such a light scanning apparatus, too.
2. Related Art
It is conventionally proposed that a light scanning apparatus has a resonance-type oscillation mirror formed using a micromachining technique as a deflector. Such an oscillation mirror has a deflecting mirror surface which is capable of oscillating about a drive shaft. As the deflecting mirror surface oscillates in sine vibration in response to a drive signal fed from outside, a light beam incident upon the deflecting mirror surface is deflected in a main scanning direction.
Further, a light detecting sensor is disposed at a predetermined location within the light scanning apparatus. Hence, it is possible to detect a light beam which moves passed one end of a scanning range for the light beam (in the vicinity of the maximum amplitude). The drive signal is controlled based on an output signal from the light detecting sensor and the angle of amplitude of the light beam is accordingly set to a predetermined value, which realizes so-called amplitude control. It is therefore necessary in amplitude control to drive the oscillation mirror such that the scanning light beam impinges upon the light detecting sensor, that is, such that the maximum amplitude of the light beam is equal to or exceeds an angle which corresponds to the location at which the light detecting sensor is disposed.
In the apparatus described in JP-A-2003-140078 for instance, a drive signal at a pre-set initial drive current (drive control variable) is fed to drive a resonance-type actuator (which corresponds to the “oscillation mirror” of the invention). The current setting value of the drive signal is gradually increases until a photo diode (i.e., a detector such as a light detecting sensor) has detected a laser beam. After detection of the laser beam, amplitude control of the laser beam is performed in accordance with the detection result. The light scanning apparatus having the structure may be installed in an image forming apparatus or the like to function as an exposure unit.